120 



MISSOURI BOTANICAL GARDEN. 





pear in the vacuole in all cases, but in or against the proto- 

 plasmic lining. 



In addition to the tannin in the more conspicuous tan- 

 niferous cells lying immediately beneath the epidermis, a 

 small amount of tannin occurs in all the parenchyma to a 

 depth of 180 to 200 microns inside the zone of steroids 

 (f. 33). This tannin is always in the form of minute drop- 

 lets scarcely ever more than 6 microns in diameters and for 

 the most part smaller than this. The cells themselves show 

 no peculiarities, and in no w r ay are differentiated from the 

 remaining parenchyma w r ithin, except in containing these 

 droplets of tannin. Thinking, upon discovery, that they 

 might be oil, I tested them with alkanet, with negative re- 

 sults. Upon allowing the section to lie over night in very 

 weak methyl blue, they became very deeply stained. Their 

 color reactions are identical w r ith the more abundant tannin 

 of the hypodermal or idioplast layers, but they are not con- 

 spicuous on account of their small size. Their occurrence 

 does not extend as far as the idioplast layer, nor do any 

 of the parenchyma cells near to this layer show the pres- 

 ence of tannin droplets. 



Origin — Indications of this tannin zone are to be seen after 

 pollination. One week thereafter, distinctly differentiated 

 hypodermal columnar or cubical tanniferous cells may be 

 seen, though as yet the zone is not continuous. At the time 

 of pollination, these cells are not yet differentiated, but the 

 epidermis shows a diffused tannin reaction. With the dying 

 back of the stigma and very short style, the tannin cells ap- 

 pear rapidly. These cells, constituting the hypodermal tan- 

 nin zone, are sharply differentiated once for all, and differ 

 from the idioplasts only in their lack of special structural 

 character. They are distinguishable only by their contents. 



Sub-hypodermal tanniferous zone (f. 32). This zone is 

 composed of large idioplasts (giant cells 12 ) and is of vary- 

 ing thickness (1 mm. more or less), lying about 1 mm. be- 

 low the surface of the carpel. 13 The layer is four to six cells 



12 So called by Swingle, according to Howard I. c. 



13 The character of the zone varies considerably with the race. A 

 few of the difference are illustrated by Vinson, 1910. 



